In twin rotor screw compressors, the pressure gradient is normally in one direction during operation such that fluid pressure tends to force the rotors towards the suction side. The rotors are conventionally mounted in bearings at each end so as to provide both radial and axial restraint. The end clearance of the rotors at the discharge side is critical to sealing and the fluid pressure tends to force open the clearance. Also, the axial forces tend to drive the suction end of the rotors into the casing which can damage the rotors if contact between the rotor(s) and casing is allowed to occur. The need for bearings, specifically thrust bearings, adds significantly to the cost, complicates manufacturing/assembly, and add maintenance requirements.